With the spread of small portable electric and electronic equipment, small-sized and high-capacity nonaqueous secondary batteries have been extensively developed. The nonaqueous secondary batteries generally use lithium manganate, lithium cobaltate, lithium nickelate, etc. as a cathode material and a carbonaceous material, metallic lithium, etc. as an anode material.
It is difficult for the carbonaceous materials, the theoretical discharge capacity of which is as low as 372 mAh/g, to meet the increasing demands coping with the expected increase in power consumption accompanying the tendency of small electrical and electronic equipment toward multifunctionality.
Although metallic lithium has a theoretical discharge capacity as high as 3860 mAh/g, it involves the following problems. It undergoes deterioration due to reaction with the nonaqueous electrolytic solution. It grows dendritically from the anode through repetition of charge and discharge, and the dendrites ultimately penetrate the separator (insulator) to cause an internal short-circuit of the battery. The cycle life is therefore short.
To solve these problems, an anode comprising a current collector, such as a copper plate, laminated with a tin or tin alloy film by electroplating has been proposed (see JP-A-2001-68094, JP-A-2001-68095, and Preprints of The 45th Battery Symposium in Japan, p. 282, 284 & 288). Such an anode has a disadvantage that the tin or tin alloy film cracks with repetition of lithium intercalation and deintercalation and eventually falls off the current collector such as a copper plate, resulting in a failure to achieve prolongation of life. As In particular, formation of a current collector and plating with tin or a tin alloy are usually carried out separately, plating with tin or a tin alloy is proceeded after formation of an oxide film on the surface of the current collector. It follows that the tin or tin alloy film easily peels and falls off the current collector.
Additionally, an anode for nonaqueous secondary batteries has been required to have a high energy density per unit volume and unit weight.